Organic Electroluminescent materials and devices

ABSTRACT

Novel tricarbazole compounds are provided. By appropriately selecting the nature of the tricarbazole substituents, compounds with appropriate HOMO and LUMO energies can be obtained for use as materials in a secondary hole transport layer.

The claimed invention was made by, on behalf of, and/or in connection with one or more of the following parties to a joint university corporation research agreement: Regents of the University of Michigan, Princeton University, The University of Southern California, and the Universal Display Corporation. The agreement was in effect on and before the date the claimed invention was made, and the claimed invention was made as a result of activities undertaken within the scope of the agreement.

FIELD OF THE INVENTION

The present invention relates to novel tricarbazole compounds. In particular, these compounds are useful as materials that can be incorporated into a secondary hole transport layer in OLED devices.

BACKGROUND

Opto-electronic devices that make use of organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. Examples of organic opto-electronic devices include organic light emitting devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, illumination, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full color display. Industry standards for such a display call for pixels adapted to emit particular colors, referred to as “saturated” colors. In particular, these standards call for saturated red, green, and blue pixels. Color may be measured using CIE coordinates, which are well known to the art.

One example of a green emissive molecule is tris(2-phenylpyridine) iridium, denoted Ir(ppy)₃, which has the following structure:

In this, and later figures herein, we depict the dative bond from nitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as well as small molecule organic materials that may be used to fabricate organic opto-electronic devices. “Small molecule” refers to any organic material that is not a polymer, and “small molecules” may actually be quite large. Small molecules may include repeat units in some circumstances. For example, using a long chain alkyl group as a substituent does not remove a molecule from the “small molecule” class. Small molecules may also be incorporated into polymers, for example as a pendent group on a polymer backbone or as a part of the backbone. Small molecules may also serve as the core moiety of a dendrimer, which consists of a series of chemical shells built on the core moiety. The core moiety of a dendrimer may be a fluorescent or phosphorescent small molecule emitter. A dendrimer may be a “small molecule,” and it is believed that all dendrimers currently used in the field of OLEDs are small molecules.

As used herein, “top” means furthest away from the substrate, while “bottom” means closest to the substrate. Where a first layer is described as “disposed over” a second layer, the first layer is disposed further away from substrate. There may be other layers between the first and second layer, unless it is specified that the first layer is “in contact with” the second layer. For example, a cathode may be described as “disposed over” an anode, even though there are various organic layers in between.

As used herein, “solution processible” means capable of being dissolved, dispersed, or transported in and/or deposited from a liquid medium, either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed that the ligand directly contributes to the photoactive properties of an emissive material. A ligand may be referred to as “ancillary” when it is believed that the ligand does not contribute to the photoactive properties of an emissive material, although an ancillary ligand may alter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled in the art, a first “Highest Occupied Molecular Orbital” (HOMO) or “Lowest Unoccupied Molecular Orbital” (LUMO) energy level is “greater than” or “higher than” a second HOMO or LUMO energy level if the first energy level is closer to the vacuum energy level. Since ionization potentials (IP) are measured as a negative energy relative to a vacuum level, a higher HOMO energy level corresponds to an IP having a smaller absolute value (an IP that is less negative). Similarly, a higher LUMO energy level corresponds to an electron affinity (EA) having a smaller absolute value (an EA that is less negative). On a conventional energy level diagram, with the vacuum level at the top, the LUMO energy level of a material is higher than the HOMO energy level of the same material. A “higher” HOMO or LUMO energy level appears closer to the top of such a diagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled in the art, a first work function is “greater than” or “higher than” a second work function if the first work function has a higher absolute value. Because work functions are generally measured as negative numbers relative to vacuum level, this means that a “higher” work function is more negative. On a conventional energy level diagram, with the vacuum level at the top, a “higher” work function is illustrated as further away from the vacuum level in the downward direction. Thus, the definitions of HOMO and LUMO energy levels follow a different convention than work functions.

More details on OLEDs, and the definitions described above, can be found in U.S. Pat. No. 7,279,704, which is incorporated herein by reference in its entirety.

SUMMARY OF THE INVENTION

In one aspect, a compound having the formula:

Formula I is provided. In the compound of Formula I, Z is selected from the group consisting of:

X is selected from the group consisting of NR, O, S, and Se, R₁ to R₁₁ independently represent mono, di, tri, tetra substitution, or no substitution, and R and R₁ and R₁₁ are each independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one aspect, R₁ to R₁₁ represent no substitution. In one aspect, R₁ to R₁₁ are independently aryl or heteroaryl.

In one aspect, the compound has the formula:

In one aspect, the compound has the formula:

In one aspect, the compound has the formula:

In one aspect, X is O or S. In one aspect, R₂ and R₅ represent no substitution. In one aspect, R is selected from the group consisting of alkyl, heteroalkyl, aralkyl, aryl and heteroaryl.

In one aspect, the compound is selected from the group consisting of:

In one aspect, a first device is provided. The first device comprises a first organic light emitting device, further comprising: an anode, a cathode, a hole injection layer disposed between the anode and the emissive layer, a first hole transport layer disposed between the hole injection layer and the emissive layer, and a second hole transport layer disposed between the first hole transport layer and the emissive layer, wherein the second hole transport layer comprises a compound of formula:

Formula II. In the compound of Formula II, Ar comprises aryl or heteroaryl, R₁ to R₈ independently represent mono, di, tri, tetra substitution, or no substitution, and R₁ to R₈ are each independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one aspect, the second hole transport layer is disposed adjacent to the first hole transport layer. In one aspect, the first hole transport layer is thicker than the second hole transport layer.

In one aspect, Ar is selected from the group consisting of:

In one aspect, the compound has the formula:

Formula I. In the compound of Formula I, Z is selected from the group consisting of:

X is selected from the group consisting of NR, O, S, and Se, R₉, R₁₀, and R₁₁ independently represent mono, di, tri, tetra substitution, or no substitution, and R, R₉, R₁₀, and R₁₁ are each independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one aspect, the first hole transport layer comprises a compound with the formula:

wherein Ar_(a), Ar_(b), Ar_(c) and Ar_(d) are independently selected from the group consisting of aryl and heteroaryl.

In one aspect, the triplet energy of the compound of Formula II is higher than the emission energy of the emissive layer.

In one aspect, the first device further comprises an emissive dopant comprising a transition metal complex having at least one ligand or part of the ligand if the ligand is more than bidentate selected from the group consisting of:

wherein R_(a), R_(b), R_(c), and R_(d) may represent mono, di, tri, or tetra substitution, or no substitution, wherein R_(a), R_(b), R_(c), and R_(d) are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfonyl, sulfonyl, phosphino, and combinations thereof; and wherein two adjacent substituents of R_(a), R_(b), R_(c), and R_(d) are optionally joined to form a fused ring or form a multidentate ligand.

In one aspect, the first device is a consumer product. In one aspect, the first device is an organic light-emitting device. In one aspect, the first device comprises a lighting panel.

In one aspect, a first device comprising an organic light emitting device, further comprising: an anode, a cathode, a first organic layer disposed between the anode and the cathode; and wherein the first organic layer comprises a compound of formula:

Formula I. In the compound of Formula I, Z is selected from the group consisting of:

X is selected from the group consisting of NR, O, S, and Se, R₁ to R₁₁ independently represent mono, di, tri, tetra substitution, or no substitution; and R, and R₁ to R₁₁ are each independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one aspect, the first organic layer is an emissive layer. In one aspect, the emissive layer is a phosphorescent emissive layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does not have a separate electron transport layer.

FIG. 3 shows a compound of Formula I.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed between and electrically connected to an anode and a cathode. When a current is applied, the anode injects holes and the cathode injects electrons into the organic layer(s). The injected holes and electrons each migrate toward the oppositely charged electrode. When an electron and hole localize on the same molecule, an “exciton,” which is a localized electron-hole pair having an excited energy state, is formed. Light is emitted when the exciton relaxes via a photoemissive mechanism. In some cases, the exciton may be localized on an excimer or an exciplex. Non-radiative mechanisms, such as thermal relaxation, may also occur, but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from their singlet states (“fluorescence”) as disclosed, for example, in U.S. Pat. No. 4,769,292, which is incorporated by reference in its entirety. Fluorescent emission generally occurs in a time frame of less than 10 nanoseconds.

More recently, OLEDs having emissive materials that emit light from triplet states (“phosphorescence”) have been demonstrated. Baldo et al., “Highly Efficient Phosphorescent Emission from Organic Electroluminescent Devices,” Nature, vol. 395, 151-154, 1998; (“Baldo-I”) and Baldo et al., “Very high-efficiency green organic light-emitting devices based on electrophosphorescence,” Appl. Phys. Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporated by reference in their entireties. Phosphorescence is described in more detail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporated by reference.

FIG. 1 shows an organic light emitting device 100. The figures are not necessarily drawn to scale. Device 100 may include a substrate 110, an anode 115, a hole injection layer 120, a hole transport layer 125, an electron blocking layer 130, an emissive layer 135, a hole blocking layer 140, an electron transport layer 145, an electron injection layer 150, a protective layer 155, a cathode 160, and a barrier layer 170. Cathode 160 is a compound cathode having a first conductive layer 162 and a second conductive layer 164. Device 100 may be fabricated by depositing the layers described, in order. The properties and functions of these various layers, as well as example materials, are described in more detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which are incorporated by reference.

More examples for each of these layers are available. For example, a flexible and transparent substrate-anode combination is disclosed in U.S. Pat. No. 5,844,363, which is incorporated by reference in its entirety. An example of a p-doped hole transport layer is m-MTDATA doped with F.sub.4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. Examples of emissive and host materials are disclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which is incorporated by reference in its entirety. An example of an n-doped electron transport layer is BPhen doped with Li at a molar ratio of 1:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. U.S. Pat. Nos. 5,703,436 and 5,707,745, which are incorporated by reference in their entireties, disclose examples of cathodes including compound cathodes having a thin layer of metal such as Mg:Ag with an overlying transparent, electrically-conductive, sputter-deposited ITO layer. The theory and use of blocking layers is described in more detail in U.S. Pat. No. 6,097,147 and U.S. Patent Application Publication No. 2003/0230980, which are incorporated by reference in their entireties. Examples of injection layers are provided in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety. A description of protective layers may be found in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210, a cathode 215, an emissive layer 220, a hole transport layer 225, and an anode 230. Device 200 may be fabricated by depositing the layers described, in order. Because the most common OLED configuration has a cathode disposed over the anode, and device 200 has cathode 215 disposed under anode 230, device 200 may be referred to as an “inverted” OLED. Materials similar to those described with respect to device 100 may be used in the corresponding layers of device 200. FIG. 2 provides one example of how some layers may be omitted from the structure of device 100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided by way of non-limiting example, and it is understood that embodiments of the invention may be used in connection with a wide variety of other structures. The specific materials and structures described are exemplary in nature, and other materials and structures may be used. Functional OLEDs may be achieved by combining the various layers described in different ways, or layers may be omitted entirely, based on design, performance, and cost factors. Other layers not specifically described may also be included. Materials other than those specifically described may be used. Although many of the examples provided herein describe various layers as comprising a single material, it is understood that combinations of materials, such as a mixture of host and dopant, or more generally a mixture, may be used. Also, the layers may have various sublayers. The names given to the various layers herein are not intended to be strictly limiting. For example, in device 200, hole transport layer 225 transports holes and injects holes into emissive layer 220, and may be described as a hole transport layer or a hole injection layer. In one embodiment, an OLED may be described as having an “organic layer” disposed between a cathode and an anode. This organic layer may comprise a single layer, or may further comprise multiple layers of different organic materials as described, for example, with respect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used, such as OLEDs comprised of polymeric materials (PLEDs) such as disclosed in U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated by reference in its entirety. By way of further example, OLEDs having a single organic layer may be used. OLEDs may be stacked, for example as described in U.S. Pat. No. 5,707,745 to Forrest et al, which is incorporated by reference in its entirety. The OLED structure may deviate from the simple layered structure illustrated in FIGS. 1 and 2. For example, the substrate may include an angled reflective surface to improve out-coupling, such as a mesa structure as described in U.S. Pat. No. 6,091,195 to Forrest et al., and/or a pit structure as described in U.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated by reference in their entireties.

Unless otherwise specified, any of the layers of the various embodiments may be deposited by any suitable method. For the organic layers, preferred methods include thermal evaporation, ink-jet, such as described in U.S. Pat. Nos. 6,013,982 and 6,087,196, which are incorporated by reference in their entireties, organic vapor phase deposition (OVPD), such as described in U.S. Pat. No. 6,337,102 to Forrest et al., which is incorporated by reference in its entirety, and deposition by organic vapor jet printing (OVJP), such as described in U.S. patent application Ser. No. 10/233,470, which is incorporated by reference in its entirety. Other suitable deposition methods include spin coating and other solution based processes. Solution based processes are preferably carried out in nitrogen or an inert atmosphere. For the other layers, preferred methods include thermal evaporation. Preferred patterning methods include deposition through a mask, cold welding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819, which are incorporated by reference in their entireties, and patterning associated with some of the deposition methods such as ink-jet and OVJD. Other methods may also be used. The materials to be deposited may be modified to make them compatible with a particular deposition method. For example, substituents such as alkyl and aryl groups, branched or unbranched, and preferably containing at least 3 carbons, may be used in small molecules to enhance their ability to undergo solution processing. Substituents having 20 carbons or more may be used, and 3-20 carbons is a preferred range. Materials with asymmetric structures may have better solution processibility than those having symmetric structures, because asymmetric materials may have a lower tendency to recrystallize. Dendrimer substituents may be used to enhance the ability of small molecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the present invention may further optionally comprise a barrier layer. One purpose of the barrier layer is to protect the electrodes and organic layers from damaging exposure to harmful species in the environment including moisture, vapor and/or gases, etc. The barrier layer may be deposited over, under or next to a substrate, an electrode, or over any other parts of a device including an edge. The barrier layer may comprise a single layer, or multiple layers. The barrier layer may be formed by various known chemical vapor deposition techniques and may include compositions having a single phase as well as compositions having multiple phases. Any suitable material or combination of materials may be used for the barrier layer. The barrier layer may incorporate an inorganic or an organic compound or both. The preferred barrier layer comprises a mixture of a polymeric material and a non-polymeric material as described in U.S. Pat. No. 7,968,146, PCT Pat. Application Nos. PCT/US2007/023098 and PCT/US2009/042829, which are herein incorporated by reference in their entireties. To be considered a “mixture”, the aforesaid polymeric and non-polymeric materials comprising the barrier layer should be deposited under the same reaction conditions and/or at the same time. The weight ratio of polymeric to non-polymeric material may be in the range of 95:5 to 5:95. The polymeric material and the non-polymeric material may be created from the same precursor material. In one example, the mixture of a polymeric material and a non-polymeric material consists essentially of polymeric silicon and inorganic silicon.

Devices fabricated in accordance with embodiments of the invention may be incorporated into a wide variety of consumer products, including flat panel displays, computer monitors, medical monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads up displays, fully transparent displays, flexible displays, laser printers, telephones, cell phones, personal digital assistants (PDAs), laptop computers, digital cameras, camcorders, viewfinders, micro-displays, vehicles, a large area wall, theater or stadium screen, or a sign. Various control mechanisms may be used to control devices fabricated in accordance with the present invention, including passive matrix and active matrix. Many of the devices are intended for use in a temperature range comfortable to humans, such as 18 degrees C. to 30 degrees C., and more preferably at room temperature (20-25 degrees C.).

The materials and structures described herein may have applications in devices other than OLEDs. For example, other optoelectronic devices such as organic solar cells and organic photodetectors may employ the materials and structures. More generally, organic devices, such as organic transistors, may employ the materials and structures.

The terms halo, halogen, alkyl, cycloalkyl, alkenyl, alkynyl, arylkyl, heterocyclic group, aryl, aromatic group, and heteroaryl are known to the art, and are defined in U.S. Pat. No. 7,279,704 at cols. 31-32, which are incorporated herein by reference.

In one embodiment, a compound having the formula:

Formula I is provided. In the compound of Formula I, Z is selected from the group consisting of:

X is selected from the group consisting of NR, O, S, and Se, R₁ to R₁₁ independently represent mono, di, tri, tetra substitution, or no substitution, and R and R₁ to R₁₁ are each independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one embodiment, R₁ to R₁₁ represent no substitution. In one embodiment, R₁ to R₁₁ are independently aryl or heteroaryl.

In one embodiment, the compound has the formula:

In one embodiment, the compound has the formula:

In one embodiment, the compound has the formula:

In one embodiment, X is O or S. In one embodiment, R₂ and R₅ represent no substitution. In one embodiment, R is selected from the group consisting of alkyl, heteroalkyl, aralkyl, aryl and heteroaryl.

In one embodiment, the compound is selected from the group consisting of:

In one embodiment, a first device is provided. The first device comprises a first organic light emitting device, further comprising: an anode, a cathode, a hole injection layer disposed between the anode and the emissive layer, a first hole transport layer disposed between the hole injection layer and the emissive layer, and a second hole transport layer disposed between the first hole transport layer and the emissive layer, wherein the second hole transport layer comprises a compound of formula:

Formula II. In the compound of Formula II, Ar comprises aryl or heteroaryl, R₁ to R₈ independently represent mono, di, tri, tetra substitution, or no substitution, and R₁ to R₈ are each independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfonyl, sulfonyl, phosphino, and combinations thereof.

In one embodiment, the second hole transport layer is disposed adjacent to the first hole transport layer. By “adjacent” it is meant that the second hole transport layer is physically in contact with the first hole transport layer. In one embodiment, the first hole transport layer is thicker than the second hole transport layer.

As used herein, a hole transporting layer (HTL) in an OLED can be disposed between the and anode and the emissive layer. It is preferred that the HTL is relatively hole conductive, which helps avoid high operating voltage. In order to achieve high hole conductivity, high hole mobility materials are used. These materials are usually triarylamine compounds. These compounds may have HOMO/LUMO levels and/or triplet energy which are not compatible with the emissive layer for optimum device performance and lifetime. On the other hand, in order to have an HTL with more compatible HOMO/LUMO levels and/or triplet energy, hole mobility may be compromised.

In order to achieve a low voltage, higher device performance and lifetime device, the introduction of a secondary hole transporting layer, in addition to the primary hole transporting layer has been demonstrated and shown to be effective. The primary hole transporting layer is largely responsible for hole transport. The secondary hole transporting layer, sandwiched between the primary hole transporting layer and the emissive layer, functions as a bridging layer. The thickness of the secondary hole transport layer is preferably low in order to not significantly increase the operating voltage. However, the hole injection from the secondary hole transporting layer to the emissive layer, charge confinement and excition confinement between the secondary hole transporting layer and the emissive layer are controlled by the energy levels and single/triplet energy of the secondary hole transporting layer. Since the secondary hole transporting layer thickness is low, there is relatively little concern about the hole mobility. This allows for a higher flexibility in the design of materials with appropriate energy levels and single/triplet energy to function well with the emissive layer.

It has surprisingly been discovered that compounds of Formula I and II can be effectively used as materials in the secondary hole transporting layer, thereby improving the properties of the OLED devices in which they are incorporated.

In one embodiment, Ar is selected from the group consisting of:

In some embodiments, Ar is selected from the group consisting of:

In some embodiments, the compound is selected from Compounds 1-15, whose structure is depicted in the table below:

Ar Compound Ar-1 1 Ar-2 2 Ar-3 3 Ar-4 4 Ar-5 5 Ar-6 6 Ar-7 7 Ar-8 8 Ar-9 9 Ar-10 10 Ar-11 11 Ar-12 12 Ar-13 13 Ar-14 14 Ar-15 15

In one embodiment, the compound has the formula:

Formula I. In the compound of Formula I, Z is selected from the group consisting of:

X is selected from the group consisting of NR, O, S, and Se, R₉, R₁₀, and R₁₁ independently represent mono, di, tri, tetra substitution, or no substitution, and R, R₉, R₁₀, and R₁₁ are each independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one embodiment, the first hole transport layer comprises a compound with the formula:

wherein Ar_(a), Ar_(b), Ar_(c) and Ar_(d) are independently selected from the group consisting of aryl and heteroaryl.

In one embodiment, the triplet energy of the compound of Formula II is higher than the emission energy of the emissive layer.

In one embodiment, the first device further comprises an emissive dopant comprising a transition metal complex having at least one ligand or part of the ligand if the ligand is more than bidentate selected from the group consisting of:

wherein R_(a), R_(b), R_(c), and R_(d) may represent mono, di, tri, or tetra substitution, or no substitution, wherein R_(a), R_(b), R_(c), and R_(d) are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and wherein two adjacent substituents of R_(a), R_(b), R_(c), and R_(d) are optionally joined to form a fused ring or form a multidentate ligand.

In one embodiment, the first device is a consumer product. In one embodiment, the first device is an organic light-emitting device. In one embodiment, the first device comprises a lighting panel.

In one embodiment, a first device comprising an organic light emitting device, further comprising: an anode, a cathode, a first organic layer disposed between the anode and the cathode; and wherein the first organic layer comprises a compound of formula:

Formula I. In the compound of Formula I, Z is selected from the group consisting of:

X is selected from the group consisting of NR, O, S, and Se, R₁ to R₁₁ independently represent mono, di, tri, tetra substitution, or no substitution; and R, and R₁ to R₁₁ are each independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one embodiment, the first organic layer is an emissive layer. In one embodiment, the emissive layer is a phosphorescent emissive layer.

DEVICE EXAMPLES

A device examples were fabricated by high vacuum (<10⁻⁷ Torr) thermal evaporation (VTE). The anode electrode is ˜800 Å of indium tin oxide (ITO). The cathode electrode consisted of 10 Å of LiF followed by 1,000 Å of Al. All devices were encapsulated with a glass lid sealed with an epoxy resin in a nitrogen glove box (<1 ppm of H₂O and O₂) and a moisture getter was incorporated inside the package.

The organic stack of the Device Examples 1-5 in Table 1 consists of sequentially, from the ITO surface, 100 Å of LG101 (obtained from LG Chemical) as the hole injection layer (HIL), 500 Å (Table 1) of NPD as the primary hole transporting layer (HTL), 50 Å of the secondary hole transporting layer, 300 Å of Compound C or Compound D doped with 10% or 12% of phosphorescent emitter Compound E as the emissive layer (EML), 50 Å of Compound C or Compound D as the ETL2 and 450 Å of Alq₃ as the ETL1.

Device Example 6 was fabricated in the same way as in Device Examples 1-5 except that the EML layer has 3 components: 85% of Compound D, 10% of Compound 9.5% of Compound E.

Device Example 7-8 was fabricated in the same way as in Device Examples 6 except there was no secondary hole transporting layer, and the primary hole transporting layer thickness was increased to 550 Å to match the combined thickness of the primary and secondary hole transporting layers in the Device Examples 1-5.

Comparative Device Examples 1-3 were fabricated in the same way as Device Examples 1-5 except that there was no secondary hole transporting layer, and the primary hole transporting layer thickness was increased to 550 Å to match the combined thickness of the primary and secondary hole transporting layers in the Device Examples 1-5.

The organic stack of the Device Examples 9-13 and Comparative Device Example 4 in Table 2 consists of sequentially, from the ITO surface, 100 Å of LG101 as the hole injection layer (HIL), 200 Å (Table 1) of NPD as the hole transporting layer (HTL), 50 Å of the secondary hole transporting layer, 300 Å of Compound A or Compound B doped with 18% or 20% of phosphorescent emitter Compound F as the emissive layer (EML), 50 Å of Compound A as the ETL2 and 350 Å of Alq₃ as the ETL1.

Comparative Device Examples 4 was fabricated in the same way as Device Examples 9-13 except that there was no the secondary hole transporting layer, and the primary hole transporting layer thickness was increased to 250 Å to match the combined thickness of the primary and secondary hole transporting layers in the Device Examples.

The structures of the aforementioned device components are as follows:

TABLE 1 Device performance and lifetime summary of green devices At L = 1000 cd/m² At J = 40 mA/cm2 Secondary ETL2 1931 CIE Voltage LE EQE PE L₀ LT₈₀ Example HTL 50 Å EML 300 Å 50 Å x y [V] [cd/A] [%] [lm/W] [cd/m²] [h] Device Cmpd 5 Cmpd C:Cmpd Cmpd C 0.32 0.63 4.7 75 20.6 50.2 24884 340 Example 1 E 10% Device Cmpd 9 Cmpd D:Cmpd Cmpd D 0.34 0.62 5.3 72 19.8 42.4 23396 330 Example 2 E 10% Device Cmpd 13 Cmpd D:Cmpd Cmpd D 0.33 0.63 5.3 72.2 19.8 43.2 23762 250 Example 3 E 12% Device Cmpd 14 Cmpd C:Cmpd Cmpd C 0.33 0.62 5 76.5 20.9 48.3 25911 266 Example 4 E 12% Device Cmpd 15 Cmpd C:Cmpd Cmpd C 0.32 0.63 4.8 76.3 21 49.6 25722 303 Example 5 E 10% Device Cmpd 9 Cmpd D:Cmpd Cmpd D 0.33 0.62 5.8 69 19.1 37.6 22556 268 Example 6 9 10%:Cmpd E 5% Device none Cmpd D:Cmpd Cmpd D 0.32 0.63 5.8 60 16.5 32.7 17508 288 Example 7 9 10%:Cmpd E 5% Device none Cmpd D:Cmpd Cmpd D 0.32 0.63 5.5 62.8 17.3 35.8 19333 350 Example 8 13 10%:Cmpd E 5% Comparative none Cmpd C:Cmpd Cmpd C 0.33 0.63 4.9 68.1 18.6 43.8 19596 290 Device E 12% Example 1 Comparative none Cmpd D:Cmpd Cmpd D 0.32 0.63 5.2 64.3 17.6 38.8 18627 270 Device E 12% Example 2 Comparative none Cmpd D:Cmpd Cmpd D 0.33 0.62 5.3 63 17.5 37.7 17863 295 Device E 10% Example 3

TABLE 2 Device performance and lifetime summary of blue devices At L = 1000 cd/m² At J = 40 mA/cm2 Secondary 1931 CIE Voltage LE EQE PE L₀ LT₈₀ Example HTL 50 Å EML 300 Å ETL2 50 Å x y [V] [cd/A] [%] [lm/W] [cd/m²] [h] Device Cmpd 14 Cmpd A:Cmpd Cmpd A 0.18 0.39 6.1 54.5 24 28.2 9528 25 Example 9 F 18% Device Cmpd 15 Cmpd B:Cmpd Cmpd A 0.18 0.40 5.9 58.3 25.3 30.9 10010 32 Example 10 F 20% Device Cmpd 5 Cmpd B:Cmpd Cmpd A 0.18 0.40 5.7 57.9 25.2 31.7 9978 32 Example 11 F 20% Device Cmpd 13 Cmpd B:Cmpd Cmpd A 0.18 0.40 6.5 46.1 20 22.3 7472 47 Example 12 F 20% Device Cmpd 9 Cmpd A:Cmpd Cmpd A 0.18 0.39 5.7 51.3 22.7 28.1 8860 35 Example 13 F 18% Comparative none Cmpd A:Cmpd Cmpd A 0.18 0.38 5.9 45.3 20.3 24.2 7357 52 Device F 18% Example 4

As shown in Table 1, devices containing a secondary HTL (Device Examples 1-6) have higher efficiency (EQE˜20%) compared to the devices without the secondary HTL (Device Examples 7-8 and Comparative Device Examples 1-3). Devices with the secondary HTL (Device Examples 1-6) also have higher lifetimes, similar to or better than the devices without the secondary HTL (Device Examples 7-8 and Comparative Device Examples 1-3). For example, LT₈₀ (the time required for the initial luminance (L₀) to drop to 80% of its initial value, at a constant current density of 40 mA/cm²) is ˜340 at L₀=24884 cd/m² for Device Example 1 compared to 290 h at L₀=19596 cd/m² for Comparative Device Example 1. At the same time, Device Example 1 has a higher efficiency (EQE=20.6%) compared to Comparative Device Example 1 (EQE=18.6%). The same trend is seen in comparing Device Example 2 and Comparative Device Example 3. Without being bound by theory, the improved efficiency and lifetime in the presence of the secondary HTL is believed to be due to the high triplet energy, providing improved exciton confinement, the presence of a dibenzothiophene or triphenylene group, providing a high triplet, charge stabilization moiety. The calculated triplet energies are summarized in Table 3.

TABLE 3 Calculated Triplet Energies of Compounds. Compound Triplet energy (nm)^(#) NPD 500 Compound 5 417 Compound 9 429 Compound 13 447 Compound 14 417 Compound 15 417 ^(#)Based on DFT/B3LYP/6-31g(d) optimized geometry

In addition, compounds of Formula I and Formula II can improve device performance and lifetime when used as a host or co-dopant in the EML. When used as a codopant, the compounds of Formula I and Formula II can partially carry charge. This capability can allow the device to work at a lower phosphorescence emitter concentration. For example, Device Example 8 has 10% of Compound 13 and only 5% of the phosphorescent emitter in the EML whereas Comparative Device Example has 12% of the phosphorescent emitter in the EML. Yet, the efficiencies are similar and Device Example 8 lifetime is better. The LT₈₀ of Device Example 8 (EQE=17.5%) is 350 h at L₀=19333 cd/m² compared to 290 h at L₀=19596 cd/m² for Comparative Device Example 1 (EQE=18.6%). Furthermore, since the concentration of the phosphorescent emitter in the EML is reduced in Device Example 9, the CIE is more saturated-green.

In blue devices, the effect of having a secondary HTL on efficiency is very significant. For example, Device Example 9 has a much higher efficiency (EQE=25%) compared to Comparative Device Example 4 (EQE=20.3%). LT₈₀ of Device Example 9 is 25 h at L₀=9528 cd/m² compared to 50 h at L₀=7357 cd/m² for Comparative Device Example 1.

Combination with Other Materials

The materials described herein as useful for a particular layer in an organic light emitting device may be used in combination with a wide variety of other materials present in the device. For example, emissive dopants disclosed herein may be used in conjunction with a wide variety of hosts, transport layers, blocking layers, injection layers, electrodes and other layers that may be present. The materials described or referred to below are non-limiting examples of materials that may be useful in combination with the compounds disclosed herein, and one of skill in the art can readily consult the literature to identify other materials that may be useful in combination.

HIL/HTL:

A hole injecting/transporting material to be used in the present invention is not particularly limited, and any compound may be used as long as the compound is typically used as a hole injecting/transporting material. Examples of the material include, but not limit to: a phthalocyanine or porphryin derivative; an aromatic amine derivative; an indolocarbazole derivative; a polymer containing fluorohydrocarbon; a polymer with conductivity dopants; a conducting polymer, such as PEDOT/PSS; a self-assembly monomer derived from compounds such as phosphonic acid and slime derivatives; a metal oxide derivative, such as MoO_(x); a p-type semiconducting organic compound, such as 1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; a metal complex, and a cross-linkable compounds.

Examples of aromatic amine derivatives used in HIL or HTL include, but not limit to the following general structures:

Each of Ar¹ to Ar⁹ is selected from the group consisting aromatic hydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, azulene; group consisting aromatic heterocyclic compounds such as dibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene, benzoselenophene, carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine, thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine; and group consisting 2 to 10 cyclic structural units which are groups of the same type or different types selected from the aromatic hydrocarbon cyclic group and the aromatic heterocyclic group and are bonded to each other directly or via at least one of oxygen atom, nitrogen atom, sulfur atom, silicon atom, phosphorus atom, boron atom, chain structural unit and the aliphatic cyclic group. Wherein each Ar is further substituted by a substituent selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfonyl, sulfonyl, sulfonyl, phosphino, and combinations thereof.

In one aspect, Ar¹ to Ar⁹ is independently selected from the group consisting of:

k is an integer from 1 to 20; X¹ to X⁸ is C (including CH) or N; Ar¹ has the same group defined above.

Examples of metal complexes used in HIL or HTL include, but not limit to the following general formula:

M is a metal, having an atomic weight greater than 40; (Y¹—Y²) is a bidentate ligand, Y¹ and Y² are independently selected from C, N, O, P, and S; L is an ancillary ligand; m is an integer value from 1 to the maximum number of ligands that may be attached to the metal; and m+n is the maximum number of ligands that may be attached to the metal.

In one aspect, (Y¹—Y²) is a 2-phenylpyridine derivative.

In another aspect, (Y¹—Y²) is a carbene ligand.

In another aspect, M is selected from Ir, Pt, Os, and Zn.

In a further aspect, the metal complex has a smallest oxidation potential in solution vs. Fc⁺/Fc couple less than about 0.6 V.

Host:

The light emitting layer of the organic EL device of the present invention preferably contains at least a metal complex as light emitting material, and may contain a host material using the metal complex as a dopant material. Examples of the host material are not particularly limited, and any metal complexes or organic compounds may be used as long as the triplet energy of the host is larger than that of the dopant. While the Table below categorizes host materials as preferred for devices that emit various colors, any host material may be used with any dopant so long as the triplet criteria is satisfied.

Examples of metal complexes used as host are preferred to have the following general formula:

M is a metal; (Y³—Y⁴) is a bidentate ligand, Y³ and Y⁴ are independently selected from C, N, O, P, and S; L is an ancillary ligand; m is an integer value from 1 to the maximum number of ligands that may be attached to the metal; and m+n is the maximum number of ligands that may be attached to the metal.

In one aspect, the metal complexes are:

(O—N) is a bidentate ligand, having metal coordinated to atoms O and N.

In another aspect, M is selected from Ir and Pt.

In a further aspect, (Y³—Y⁴) is a carbene ligand.

Examples of organic compounds used as host are selected from the group consisting aromatic hydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene, chrysene, perylene, azulene; group consisting aromatic heterocyclic compounds such as dibenzothiophene, dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene, benzosclenophene, carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine, benzofuropyridine, furodipyridine, benzothienopyridine, thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine; and group consisting 2 to 10 cyclic structural units which are groups of the same type or different types selected from the aromatic hydrocarbon cyclic group and the aromatic heterocyclic group and are bonded to each other directly or via at least one of oxygen atom, nitrogen atom, sulfur atom, silicon atom, phosphorus atom, boron atom, chain structural unit and the aliphatic cyclic group. Wherein each group is further substituted by a substituent selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one aspect, host compound contains at least one of the following groups in the molecule:

R¹ to R⁷ is independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphine, and combinations thereof, when it is aryl or heteroaryl, it has the similar definition as Ar's mentioned above.

k is an integer from 0 to 20.

X¹ to X⁸ is selected from C (including CH) or N.

Z¹ and Z² is selected from NR¹, O, or S.

HBL:

A hole blocking layer (HBL) may be used to reduce the number of holes and/or excitons that leave the emissive layer. The presence of such a blocking layer in a device may result in substantially higher efficiencies as compared to a similar device lacking a blocking layer. Also, a blocking layer may be used to confine emission to a desired region of an OLED.

In one aspect, compound used in BBL contains the same molecule or the same functional groups used as host described above.

In another aspect, compound used in HBL contains at least one of the following groups in the molecule:

k is an integer from 0 to 20; L is an ancillary ligand, m is an integer from 1 to 3.

ETL:

Electron transport layer (ETL) may include a material capable of transporting electrons. Electron transport layer may be intrinsic (undoped), or doped. Doping may be used to enhance conductivity. Examples of the ETL material are not particularly limited, and any metal complexes or organic compounds may be used as long as they are typically used to transport electrons.

In one aspect, compound used in ETL contains at least one of the following groups in the molecule:

R¹ is selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, when it is aryl or heteroaryl, it has the similar definition as Ar's mentioned above.

Ar¹ to Ar³ has the similar definition as Ar's mentioned above.

k is an integer from 0 to 20.

X¹ to X⁸ is selected from C (including CH) or N.

In another aspect, the metal complexes used in ETL contains, but not limit to the following general formula:

(O—N) or (N—N) is a bidentate ligand, having metal coordinated to atoms O, N or N, N; L is an ancillary ligand; m is an integer value from 1 to the maximum number of ligands that may be attached to the metal.

In any above-mentioned compounds used in each layer of the OLED device, the hydrogen atoms can be partially or fully deuterated.

In addition to and/or in combination with the materials disclosed herein, many hole injection materials, hole transporting materials, host materials, dopant materials, exiton/hole blocking layer materials, electron transporting and electron injecting materials may be used in an OLED. Non-limiting examples of the materials that may be used in an OLED in combination with materials disclosed herein are listed in Table 4 below. Table 4 lists non-limiting classes of materials, non-limiting examples of compounds for each class, and references that disclose the materials.

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Experimental

Chemical abbreviations used throughout this document are as follows: Cy is cyclohexyl, dba is dibenzylideneacetone, EtOAc is ethyl acetate, DME is dimethoxyethane, dppe is 1,2-bis(diphenylphosphino)ethane, THF is tetrahydrofuran, DMF is dimethylformamide, DCM is dichloromethane, S-Phos is dicyclohexyl(2′,6′-dimethoxy-[1,1′-biphenyl]-2-yl)phosphine, Tf is trifluoromethylsulfonate. Unless specified otherwise, references to degassing a particular solvent refer to saturating the solvent sufficiently with dry nitrogen gas (by bubbling it in the solvent) to substantially remove gaseous oxygen from the solvent.

Synthesis of 3,6-bis(9-phenylcarbazol-3-yl)carbazole

A solution of 9-phenyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)carbazole (7.1 g, 19.2 mmol), 3,6-dibromo-9H-carbazole (2.6 g, 8.0 mmol), K₂CO₃ (11.0 g, 79.7 mmol) in toluene (120 mL), water (40 mL) and EtOH (40 mL) was bubbled for 30 minutes with nitrogen. Then, Pd(PPh₃)₄ (0.9 g, 0.8 mmol) was added. The mixture was bubbled with nitrogen for 15 minutes and refluxed for 10 hours, after which bromobenzene (0.9 mL, 8.6 mmol) was added. The resultant mixture was refluxed for 6 hours. After cooling, the reaction mixture was extracted with CH₂Cl₂ and dried with MgSO₄. The solvent was removed in vacuo and the residue was purified by flash chromatography using 40-60% CH₂Cl₂/hexane to afford 3,6-bis(9-phenylcarbazol-3-yl)carbazole (3.4 g, 65% yield) as a white solid.

Synthesis of Compound 5

A solution of xylene (125 mL) was bubbled with nitrogen for 15 minutes 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (1.1 g, 2.7 mmol) and Pd₂(dba)₃ (0.6 g, 0.7 mmol) were added. The mixture was bubbled for 15 min. 3,6-bis(9-phenylcarbazol-3-yl)carbazole, 3-bromo-9-phenylcarbazole (1.0 g, 3.1 mmol), sodium tert-butoxide (0.6 g, 6.3 mmol) were added. The mixture was bubbled for 15 min. and refluxed for 15 h. After cooling, the reaction mixture was filtered through a silica pad and washed with 80% CH₂Cl₂/hexane. The solvent was removed in vacuo and the residue was purified by flash chromatography using 30-40% CH₂Cl₂/hexane to afford Compound 5 (2.3 g, 76% yield) as a white solid.

Synthesis of Compound 7

A solution of 3,6-bis(9-phenylcarbazol-3-yl)carbazole (3.61 g, 5.56 mmol) and 4-iododibenzo[b,d]furan (1.797 g, 6.11 mmol), copper(I) iodide (0.106 g, 0.556 mmol), potassium phosphate (3.54 g, 16.67 mmol) and cyclohexane-1,2-diamine (0.127 g, 1.11 mmol) in dry xylene (150 mL) was degassed and heated to reflux under N₂ for 48 hours. After cooling, the mixture was filtered and the filtrate was concentrated and purified by column chromatography on silica gel (hexane:DCM 1:1) to provided Compound 7 as a white solid (2.8 g, 62%).

Synthesis of Compound 9

A solution of xylene (125 mL) was bubbled with nitrogen for 15 minutes, then. 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (1.5 g, 3.6 mmol) and Pd₂(dba)₃ (0.8 g, 0.9 mmol) were added. The mixture was bubbled for 15 min, then 3,6-bis(9-phenylcarbazol-3-yl)carbazole (3.1 g, 4.8 mmol), 4-iododibenzo[b,d]thiophene (1.7 g, 5.5 mmol), and sodium tert-butoxide (0.9 g, 9.4 mmol) were added. The mixture was bubbled with nitrogen for 15 minutes and refluxed for 12 hours. After cooling, the reaction mixture was filtered through a silica pad and washed with 80% CH₂Cl₂/hexane. The solvent was removed in vacuo and the residue was purified by flash chromatography using 30-50% CH₂Cl₂/hexane to afford Compound 9 (2.5 g, 63% yield) as a white solid.

Synthesis of Compound 13

A solution of 9-phenyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-carbazole (4.3 g, 11.7 mmol), 3,6-dibromo-9-(triphenylen-2-yl)-9H-carbazole (2.9 g, 5.3 mmol), K₃PO₄ (6.6 g, 31.1 mmol) in toluene (100 mL) and water (10 mL) was bubbled with nitrogen for 15 minutes. Then, 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (0.4 g, 1.0 mmol) and Pd₂(dba)₃ (0.2 g, 0.2 mmol) were added. The mixture was bubbled with nitrogen for 15 minutes and refluxed for 12 hours. Bromobenzene (1.0 mL, 9.5 mmol) and Pd(PPh₃)₄ (0.3 g, 0.3 mmol) were added. The resultant mixture was refluxed for 12 hours. After cooling, the reaction mixture was filtered through a short column packed with silica and MgSO₄ and washed with 80% CH₂Cl₂/hexane. The solvent was removed in vacuo and the residue was purified by flash chromatography using 45% CH₂Cl₂/hexane to afford Compound 13 (3.7 g, 80% yield) as a white solid.

Synthesis of Compound 14

A solution of xylene (125 mL) was bubbled with nitrogen for 15 min, then 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (0.8 g, 2.0 mmol) and Pd₂(dba)₃ (0.4 g, 0.5 mmol) were added. The mixture was bubbled for 15 min. 3,6-bis(9-phenylcarbazol-3-yl)carbazole (2.7 g, 4.2 mmol), 9-(4-bromophenyl)-9H-carbazole (2.4 g, 7.5 mmol), NaO^(t)Bu (1.0 g, 10.4 mmol) were added. The mixture was bubbled for 15 min. and refluxed for 10 h. After cooling, the reaction mixture was filtered through a silica pad and washed with 75% CH₂Cl₂/hexane. The solvent was removed in vacuo and the residue was purified by flash chromatography using 30-40% CH₂Cl₂/hexane to afford Compound 14 (3.4 g, 92% yield) as a white solid.

Synthesis of Compound 15

A solution of xylene (125 mL) was bubbled with nitrogen for 15 min, then 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (0.7 g, 1.7 mmol) and Pd₂(dba)₃ (0.4 g, 0.5 mmol) were added. The mixture was bubbled with nitrogen for 15 minutes, then 3,6-bis(9-phenylcarbazol-3-yl)carbazole (2.8 g, 4.3 mmol), 9-(3-bromophenyl)-9H-carbazole (2.6 g, 8.0 mmol), and sodium tert-butoxide (0.8 g, 8.3 mmol) were added. The mixture was bubbled with nitrogen for 15 minutes and refluxed for 12 hours. After cooling, the reaction mixture was filtered through a silica pad and washed with 90% CH₂Cl₂/hexane. The solvent was removed in vacuo and the residue was purified by flash chromatography using 30-50% CH₂Cl₂/hexane to afford Compound 15 (3.6 g, 94% yield) as a white solid.

It is understood that the various embodiments described herein are by way of example only, and are not intended to limit the scope of the invention. For example, many of the materials and structures described herein may be substituted with other materials and structures without deviating from the spirit of the invention. The present invention as claimed may therefore include variations from the particular examples and preferred embodiments described herein, as will be apparent to one of skill in the art. It is understood that various theories as to why the invention works are not intended to be limiting. 

The invention claimed is:
 1. A compound having the formula:

Formula I; wherein Z is selected from the group consisting of:

wherein X is selected from the group consisting of NR, O, S, and Se; wherein R₁ to R₁₁ independently represent mono, di, tri, tetra substitution, or no substitution; wherein R and R₁ to R₁₁ are each independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.
 2. The compound of claim 1, wherein R₁ to R₁₁ represent no substitution.
 3. The compound of claim 1, wherein R₁ to R₁₁ are independently aryl or heteroaryl.
 4. The compound of claim 1, wherein the compound has the formula:


5. The compound of claim 1, wherein the compound has the formula:


6. The compound of claim 1, wherein the compound has the formula:


7. The compound of claim 1, wherein X is O or S.
 8. The compound of claim 1, wherein R₂ and R₅ represent no substitution.
 9. The compound of claim 1, wherein R is selected from the group consisting of alkyl, heteroalkyl, aralkyl, aryl and heteroaryl.
 10. The compound of claim 1, wherein the compound is selected from the group consisting of:


11. A first device comprising a first organic light emitting device, further comprising: an anode; a cathode; a hole injection layer disposed between the anode and the emissive layer; a first hole transport layer disposed between the hole injection layer and the emissive layer; and a second hole transport layer disposed between the first hole transport layer and the emissive layer; wherein the second hole transport layer comprises a compound of formula:

 Formula II; wherein Ar comprises aryl or heteroaryl; wherein R₁ to R₈ independently represent mono, di, tri, tetra substitution, or no substitution; and wherein R₁ to R₈ are each independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.
 12. The first device of claim 11, wherein the second hole transport layer is disposed adjacent to the first hole transport layer.
 13. The first device of claim 11, wherein the first hole transport layer is thicker than the second hole transport layer.
 14. The first device of claim 11, wherein Ar is selected from the group consisting of:


15. The first device of claim 11, wherein the compound has the formula:

wherein Z is selected from the group consisting of:

wherein X is selected from the group consisting of NR, O, S, and Se; wherein R₉, R₁₀, and R₁₁ independently represent mono, di, tri, tetra substitution, or no substitution; and wherein R, R₉, R₁₀, and R₁₁ are each independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.
 16. The first device of claim 11, wherein the first hole transport layer comprises a compound with the formula:

wherein Ar_(a), Ar_(b), Ar_(c) and Ar_(d) are independently selected from the group consisting of aryl and heteroaryl.
 17. The first device of claim 11, wherein the triplet energy of the compound of Formula II is higher than the emission energy of the emissive layer.
 18. The first device of claim 11, further comprising an emissive dopant comprising a transition metal complex having at least one ligand or part of the ligand if the ligand is more than bidentate selected from the group consisting of:

wherein R_(a), R_(b), R_(c), and R_(d) may represent mono, di, tri, or tetra substitution, or no substitution; wherein R_(a), R_(b), R_(c), and R_(d) are independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and wherein two adjacent substituents of R_(a), R_(b), R_(c), and R_(d) are optionally joined to form a fused ring or form a multidentate ligand.
 19. The first device of claim 11, wherein the first device is a consumer product.
 20. The first device of claim 11, wherein the first device is an organic light-emitting device.
 21. The first device of claim 11, wherein the first device comprises a lighting panel.
 22. A first device comprising an organic light emitting device, further comprising: an anode; a cathode; a first organic layer disposed between the anode and the cathode; and wherein the first organic layer comprises a compound of formula:

 Formula I; wherein Z is selected from the group consisting of:

wherein X is selected from the group consisting of NR, O, S, and Se; wherein R₁ to R₁₁ independently represent mono, di, tri, tetra substitution, or no substitution; and wherein R, and R₁ to R₁₁ are each independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof.
 23. The first device of claim 22, wherein the first organic layer is an emissive layer.
 24. The first device of claim 23, wherein the emissive layer is a phosphorescent emissive layer. 